Now my ship is showing 5 slots in miscellaneous devices.
I have installed 3: cargo hold expansion, dollar panel array and drive upgrade.
2 slots are still empty, labelled reactor slot and device slot.
However, trying to install anything there, I get message, your ship does not have an open device slot for this device.
What am I missing here?

I do carry 2 cannons, and also a missile rack with one weapon slot empty. But this too is reporting to be not open?

So I do have 6 installed devices, but of different categories. Is this how it is supposed to be? 1 initial weapon +5 additional slots, 6 altogether?

If it is, is there any mod that bypasses this limitation, this is completely killing my game enjoyment.

Now my ship is showing 5 slots in miscellaneous devices.
I have installed 3: cargo hold expansion, dollar panel array and drive upgrade.
2 slots are still empty, labelled reactor slot and device slot.
However, trying to install anything there, I get message, your ship does not have an open device slot for this device.
What am I missing here?

I do carry 2 cannons, and also a missile rack with one weapon slot empty. But this too is reporting to be not open?

So I do have 6 installed devices, but of different categories. Is this how it is supposed to be? 1 initial weapon +5 additional slots, 6 altogether?

If it is, is there any mod that bypasses this limitation, this is completely killing my game enjoyment.

I'm carrying a fast fire laser cannon and Rasiermesser smart cannon.
So 3 weapons + 3 mics devices =6, that means Osaka is 6 devices not 5?
But if the reactor does not count, then why am I not able to purchase an upgrade? It is showing no open slots.

additional question, what is Tempus lab? I'm only on my second system, this lab is there, but it does not want to do any business with me.

No, most ships have 8 slots, the EI500 has 9, and the Osaka only has 7. The information on the ship selection screen only tells you how many are free, not the total. In general, reactors count as devices, but until recently, all player ships started with a built-in reactor that didn't take up a slot. All the other ships have been updated so that they start with a normal reactor, which takes up a slot and gets removed when you buy an upgrade, but the Osaka has not. I've already created listings on Ministry with suggestions to make this more clear and add a starting reactor to the Osaka.

Also, the graphics on the dock services screens don't show the exact number of slots you have available. There's no way they could do that because some slots can be used for more than one type of device. Also, some devices don't take up a slot, but an empty slot still has to be shown so that you can install them. Instead, they show a slot for each type of device you can only have one of, each installed device, and an empty weapon slot and miscellaneous device slot. You have to look at the text on the dock services or ship status screen to see how many slots you have free.

You have 3 weapons (2 primaries and a launcher), and 3 miscellaneous devices installed. Your reactor slot says it's empty, so you're still using the built-in reactor that the Osaka starts with. If you want to upgrade it, that will take up another slot. You don't mention a shield generator, but if you have one installed, that also takes up a slot, so you'd be full.

Installing a drive will always increase your thrust. Higher level drives add more thrust. However, a drive will only increase your top speed up to a certain limit, so if your ship already has equal or higher top speed, it won't change. The limits are:
tritium propulsion upgrade: .2 c
Titan 440 and inertialess drive: .25 c
pteracnium megadrive: .3 c

The inertialess drive also makes you accelerate instantly to your top speed in whatever direction you're facing as long as you're thrusting and stop instantly when you're not. That can be useful, but consumes a lot of fuel and is very different to pilot.